Page:Bergey's manual of determinative bacteriology.djvu/33

 :::Order V. Actinomycetales Buchanan, 1917.
 * Order VI. Caryophanales Peshkoff, 1940.
 * Order VII. Beggiatoales Buchanan, 1956.
 * Order VIII. Myxobacterales Jahn, 1911.
 * Order IX. Spirochaetales Buchanan, 1918.
 * Order X. Mycoplasmatales Freundt, 1955.
 * Class III. Microtatobiotes Philip, 1955.
 * Order I. Rickettsiales Buchanan and Buchanan, 1938, emend. Gieszczykiewicz, 1939.
 * Order II. Virales Breed, Murray and Hitchens, 1944.
 * Division II. Thallophyta Endlicher, 1836.
 * Division III. Bryophyta Haeckel, 1866.
 * Division IV. Pteridophyta Haeckel, 1866.
 * Division V. Spermatophyta Goebel, 1882.

It has been felt desirable to subdivide the Order Eubacteriales, as defined in the 6th edition of the, into Order I, Pseudomonadales, which includes all of the polar-flagellate types of true bacteria, and Order IV, Eubacteriales, which includes the peritrichous types of true bacteria. As in the 6th edition, the photosynthetic purple and green bacteria that are polar flagellate have been included in the order with the colorless polar-flagellate bacteria. This arrangement emphasizes a concept first introduced into the classification of bacteria by Migula (Arb. Bact. Inst. Karlsruhe, 1, 1894, 235-238). This concept is analogous to the concept used by protozoologists who recognize the orders Flagellata and Infusoria in Protozoa.

Bacteriologists have recognized differences between polar flagellate and peritrichous bacteria ever since Migula emphasized them, but there has always been a residual protest against drawing a sharp line between the two groups of bacteria. While there is good reason to draw a sharp line between the ordinary polar flagellate types of bacteria and the peritrichous types, there are certain groups such as legume nodule bacteria (Rhizobium), the violet bacteria (Chromobacterium), the agrobacteria (Agrobacterium) and certain motile forms placed in the family Corynebacteriaceae that present a type of peritrichous flagellation that, when studied superficially, is misleading. Some cultures of these organisms are found to show only a single flagellum, while others closely related to these monotrichous species show several flagella peritrichously arranged. On casual examination these conditions appear to form a transition between the two types of flagellation. However, this clearly is not the case. This apparently intermediate type of flagellation seems to be a comparatively recent development in which the flagella of certain peritrichously flagellated species have undergone a retrogressive specialization. In this the organisms have become primarily dependent on one flagellum as their chief organ of locomotion. They therefore are included in Order IV, Eubacteriales, with other peritrichous bacteria.